10 INTRODUCTION 



Methods of collection and study. All plankton collections have been 

 made with nets. In general both the bolting silk net and the cotton 

 disc net were used. The bolting silk net of No. 20 bolting cloth (new 

 No. 25) is that described by Juday*. The cotton disc net is made by 

 attaching a filter designed for purifying drinking water (Jones Mod- 

 ern Filter made by the Jones Mfg. Co., Boston, Mass.) to the bottom 

 of an eighteen inch cone of canvas whose mouth is held open by a light 

 metal ring ten inches in diameter. In using this filter a special cot- 

 ton disc supplied by the manufacturer is placed in the filter and the 

 whole apparatus drawn through the water. The algae collect on the 

 disc and when there is a sufficient accumulation the disc is taken from 

 the filter and shaken in a bottle with a small amount of water which 

 removes the algae. This net catches many of the smaller organisms 

 that pass through the bolting silk (the nannoplankton) and it is also 

 very useful in obtaining samples by dipping when no boat is available. 

 Whenever possible samples have been gathered by towing the nets at 

 the surface and all collections have been made in the deep parts of all 

 lakes to avoid, as far as possible, the littoral flora. No attempt has 

 been made to study the vertical distribution of the algae in any lake. 



In studying the flora of any region a field laboratory was established 

 and with that as a center excursions were made to the surrounding 

 lakes. By traveling from lake to lake in an automobile collections 

 could be made in the morning and the material studied the same after- 

 noon and the following day. In the northeastern lake area where 

 there are no roads in many cases, but where lakes are close together, 

 they can be visited by portaging a canoe from lake to lake. Collections 

 have been made from row boats, where they were obtainable, but in a 

 few instances collections had to be made by repeatedly dipping the 

 net after wading to where the water was 3-4 feet deep or from rafts. 

 Upon returning to the temporary laboratory equipped with compound 

 microscope, camera lucida, and drawing materials, the living specimens 

 were studied and numerous pencil camera lucida drawings made of all 

 doubtful, interesting, or rare organisms, together with notes on occur- 

 rence and ocular micrometer measurements of known forms. No ob- 

 servations were made on desmids or diatoms at this time. The study 

 of the Chlorophyceae, Myxophyceae and Phaeophyceae in the living 

 condition is particularly important since many of them do not preserve 

 well and certain features such as cilia, chloroplasts, and contractile 

 vacuoles are lost when material is preserved. All drawings of one 

 species are mounted on the same sheet and corresponding notes on an- 

 other. These are then filed in species and genus covers in the usual 



* Juday, C. Limnological apparatus. Trans. Wis. Acad. Sci. Arts & Lett. 

 18 s : 566-592. 1916. 



